Air-gap structure between integrated LiNbO₃ optical modulators and micromachined Si substrates

The air-gap structure between integrated LiNbO3 optical modulators and micromachined Si substrates is reported for high-speed optoelectronic systems. The calculated and experimental results show that the high permittivity of the Si substrate decreases the resonant modulation frequency to 10 GHz LiNbO ₃ resonant-type optical modulator chips on the Si substrate. To prevent this substrate effect, an air-gap was formed between the LiNbO ₃ modulator and the Si substrate. The ability to fabricate the airgap structure was demonstrated using low-temperature flip-chip bonding (100 °C) and a Si micromachining process, and its performance was experimentally verified.